1. Field of the Invention
The present invention relates to a die clamping apparatus of an injection molding machine, etc., and especially relates to a die clamping apparatus and a die clamping method wherein a movable platen is moved toward a stationary platen by a die opening/closing mechanism, and a half nut is engaged with an engaging part formed on a tie bar, so that the tie bar can be pulled by a die clamping cylinder to carry out die clamping.
2. Description of the Related Art
Conventionally, a die clamping apparatus wherein a movable platen is moved toward a stationary platen by a die opening/closing mechanism and a half nut is engaged with an engaging part formed on a tie bar, so that the tie bar is pulled by a die clamping cylinder to carry out die clamping is known, as described in Japanese Unexamined Patent Publication (Kokai) No. 10-296739, Japanese Unexamined Patent Publication (Kokai) No. 2003-181894, or Japanese Unexamined Patent Publication (Kokai) No. 8-276482. In these known die clamping apparatuses, the position of a tie bar or a half nut must be adjusted to engage the half nut with an engaging part of the tie bar, and, to this end, an adjusting mechanism is provided.
Kokai No. 10-296739 discloses, in FIG. 9, a prior art wherein a stopper is provided on a half nut, so that a movable platen and the half nut can be stopped at a position capable of engaging with a tie bar by the stopper. However, in the known apparatus disclosed in FIG. 9, because die thickness adjustment is carried out by changing a piston position of a die clamping cylinder, there is a problem that a die clamping cylinder having a long stroke is required. Also, Kokai No. 10-296739 discloses, in FIG. 10, a prior art wherein a piston position of a die clamping cylinder is adjusted by an adjusting screw and a fixed nut in accordance with a change of the die thickness, whereby a tie bar is stopped at a position capable of engaging with a half nut. However, in the art disclosed in FIG. 10, because it is necessary to manually adjust the stopping position of each tie bar, separately, it is difficult to correctly move the tie bar to the stopping position and it takes time to complete the operation. Also, in the apparatus of FIG. 10, the structure of the die clamping cylinder becomes complicated and a strong die opening operation after completion of cooling a molded product cannot be carried out by the die clamping cylinder.
Kokai No. 10-296739 also discloses in FIG. 1, etc., that a tie bar is moved by a tie bar sliding servo motor, which is provided separately from a die clamping cylinder for pulling the tie bar, and that the moving speed of a movable platen and the tie bar are synchronized to engage a threaded part of the tie bar and a half nut. However, in Kokai No. 10-296739, since the tie bar and the piston, which are heavy, must be moved at high speed upon molding, four large-capacity servo motors are required, in order to avoid overload to the servo motor for sliding the tie bar, thus leading to a great increase in the cost.
Kokai No. 2003-181984 discloses, in FIG. 1, a connecting position adjusting means which is provided separately from a die clamping cylinder for pulling a tie bar, wherein a servo motor of the connecting position adjusting means is used for adjusting and moving the position of a tie bar with respect to a movable platen. However, in the arrangement of Kokai No. 2003-181894, since the position of the tie bar is adjusted by the servo motor at the time of molding, a large-capacity servo motor is required, as in Kokai No. 10-296739.
Further, Kokai No. 8-276482 discloses an apparatus wherein a sub-cylinder, whose piston rod is connected to a ram of a die clamping cylinder for pulling a tie bar, is provided and a position of the tie bar is adjusted by the sub-cylinder so as to stop the tie bar at a position capable of engaging with a half nut. However, in the apparatus of Kokai No. 8-276482, as the stroke of the hydraulic cylinder must be finely adjusted, it takes time to complete the position adjustment of the tie bar.